Comprehension question about "Interpolation from Curve Mapping" node
This (at the first glimpse) unexpected behavior exists because otherwise you can't create certain types of interpolations. eg the 'back' interpolation with an overshoot would not be possible.

This is why AN (Animation Nodes addon) remaps the Y values: 0.25 -> 0; 0.75 -> 1

All values below 0.25 or above 0.75 will be the 'overshoot' (and you need this overshoot quite often in motion graphics..)

Fortunately, Blender draws the horizontal lines in the curve mapping editor so that it is easy to see where 0.25 and 0.75 are.

Use the Debug Interpolation node to see the mapping performed by Animation Nodes.



If the remapping would not exist, there would just not be enough space in the node ui to have control over the overshoot: